The invention relates to a method and apparatus for cutting material substrates. The apparatus described is particularly adapted for cutting flat substrates such as calendered elastomers and composite plies.
In the manufacture of tires, because of the nature of the tire building process, it is common that tire components are spliced as they are laid up on the tire building drum. The most common splice in a tire is an overlap splice, but in some constructions, butt splicing of the tire components is preferred.
One of the reasons that overlap splices are most common is that less precision is needed for an overlap splice than for a butt splice. In a butt splice, the tire component needs to be very close to the precise length needed for the component to circumvent the building drum and the tire components that have previously been applied to the building drum. If the component is too long, the butt splice creates a bulge, and if a component is too short, there will be a gap between the ends of the component on the building drum. Also, the better the precision in the butt splice, the more likely it is that the butt splice will retain its integrity as the green tire is subjected to expansion during the curing step in the tire manufacturing process.
In the early days of tire building, ply stock was often cut manually using a builder""s hot knife or an automatic plunge cut hook knife. Both these tools have the potential for cutting gum stock away from the wire when the material being cut is a reinforced composite, such as those used in making the carcass ply of the tire. For adhesion of the butted ends in a butt splice, it is preferred that some gum stock remains on the wire, preferably on both sides of the cut. To address some of the difficulties noted using manual procedures and hook knives, recent attempts to automate the cutting procedure include an automatic ply cut using a cold turning circular blade (a pizza cutter). The circular blade provides an excellent cut but has a tendency to pinch the material being cut against the cutting anvil. A pinched or rounded cut edge reduces the optimum surface area in those applications where a butt splice is used. For a butt splice, it is preferred that the two ends of the composite component be square, so that they have optimum surface area when the two square ends are stitched together in the product. Also, it is preferred that the two square ends have as much tack as possible.
An apparatus for cutting a substrate comprises a rotatable cutting wheel having heating means, temperature measuring means, and optionally temperature control means associated therewith.
In an illustrated embodiment, an apparatus for cutting a substrate comprises (a) a rotatable cutting wheel mounted on sliding means associated with a slide, (b) a hard cutting surface associated with the slide, the cutting wheel being disposed between the cutting surface and the slide, and (c) heating means, temperature measuring means and optionally a temperature control means associated with the cutting wheel. The rotatable cutting wheel is mounted on a hollow spindle and a heating means is housed within the hollow spindle, and a thermocouple associated with the rotatable cutting wheel is connected to the heating means. An electrical slip ring provides an electrical connection between a power supply and the thermocouple and heating means. The temperature control means may be a temperature control unit capable of monitoring the temperature of the cutting wheel and signaling an operator when the temperature is outside a designated range. The temperature control unit has means for increasing energy input to the heating means when the temperature drops below a specified range and decreasing the energy input to the heating means when the temperature rises above a specified range.
Since the assembly for heating the cutting wheel is heated, the hollow spindle is supported on high temperature bearings.
A hard cutting surface provided opposite the cutting wheel may be provided as an anvil integrally connected to the apparatus.
Also provided is a method for cutting a substrate comprising the steps of (a) placing a substrate on a hard surface wherein the substrate is disposed between the hard surface and a cutting wheel (b) heating the cutting wheel above room temperature to a temperature at or below the melting temperature of the substrate, thereby obtaining a heated cutting wheel, and (c) traversing the substrate with the heated cutting wheel. In the illustrated embodiment, the method further comprises the steps of mounting the cutting wheel on a slide and sliding the cutting wheel across the substrate. The method may further comprise the step of maintaining the cutting wheel at a pre-specified temperature.
Also provided is a method of making a butt splice comprising the steps of (a) heating a rotatable cutting wheel above room temperature to a temperature at or less than the melting temperature of a polymer substrate intended for use in making a butt splice (b) cutting the substrate with a heated cutting wheel and (c) laying the substrate up in a polymeric product where two cut ends of the substrate are butted against one another.
It is an object of the invention to provide apparatus and an improved cutting method for preparing substrates in a manufacturing process.
It is a further object of the invention to improve the cutting process for elastomeric and plastic materials that are used in manufacturing processes.
Other objects of the invention will be apparent from the following description and claims.